Title:Estimation of Taft ρ* of Dissociation Equilibriums of Methanium Ions RCH4+ the Hydrocarbon Super Acids: A Chemical Education Practice in Physical-Organic Chemistry Class-Room
VOLUME: 7 ISSUE: 3
Author(s):Rachura Sanjeev and Vandanapu Jagannadham*
Affiliation:Department of Chemistry, Geethanjali College of Engineering and Technology, Cheeryala-501301, Rangareddy Dist., Telangana, Department of Chemistry, Osmania University, Hyderabad-500007
Keywords:Taft reaction constant (ρ*), attenuation effect, methanium ions, super acids, protonation,
methananium ions.
Abstract:Background: In continuation from our crusade on the study of ‘attenuation effect'
in aromatic and aliphatic systems prompted us to give another attempt to estimate the Taft ρ*
value of the dissociation equilibriums (RCH4
+ ⇌ RCH3 + H+) of the methanium ion (CH5
+)
and substituted methanium ions (RCH4
+ ) based on the attenuation effect on the dissociation
equilibriums of alkyl ammonium ions (RNH3
+ ⇌ RNH2 + H+) with one, two, three, four,
five and six atoms between the ionizable proton and the first carbon atom of the substituent.
Objectives: To explain the “attenuation effect” and its applications in organic chemistry to the
graduate students.
Methods: All calculations, drawings and curve fittings were done by KaleidaGraph software
version 4.1 supplied by Synergy Software INC., Reading, PA, USA.
Results: First the dissociation equilibriums of alkyl ammonium ions with increasing carbon
chain length between the ionizable proton and the first carbon atom of the substituent were
explained. The Taft ρ* was evaluated for all the equilibriums. Finally the effect of number of
atoms between the ionizable proton and the first carbon atom of the substituent were studied.
From this the ρ* was evaluated for the equilibrium (RCH4
+ ⇌ RCH3 + H+ was evaluated.
Conclusion: Using the application of “attenuation effect” the experimentally not
determinable quantities could be determined.
